1. Field of the Invention
This invention relates to electrical circuitry providing a source of electric current and, more particularly, a current source circuit for voltage regulators used in integrated emitter coupled logic (ECL) circuits.
2. Prior Art
Some electronic circuits require a source of electric current for proper operation. In some integrated circuit technologies the current source is composed of a simple resistor having a voltage source at one end and an output terminal at the other end. To avoid the problems of variations in the output current due to fluctuations in the voltage source and the like, more elaborate circuits have been designed with active elements, such as transistors. When transistors are used, designs having transistors of mixed polarities i.e., both NPN and PNP transistors, are often employed. This is undesirable from the standpoint of integrated circuit processing since extra processing steps are often required to manufacture both polarity transistors in a single substrate. Moreover, these designs are sometimes impossible with particular process constraints.
Another problem occurs when such simple current sources are used to power voltage regulators which in turn supply voltages to the current generators of ECL circuits. With the characteristic variations in integrated circuit processing, it is difficult to determine precisely the output voltages of the ECL circuits. Variations in the voltage source also undesirably affect the responses of the ECL circuits.